Use of obtusaquinone as a fungicide to control wood-inhabiting marine fungi

ABSTRACT

A method of controlling marine fungi by which obtusaquinone of the above formula is applied to the material to be protected.   A fungicide which contains obtusaquinone,

United States Patent [191 Bultman et al.

USE OF OBTUSAQUINONE AS A FUNGICIDE T0 CONTROL WOOD-INHABITING MARINE FUNG] [75] Inventors: John D. Bultman, Oxon Hill, Md.;

Leonard Jurd, Berkley, Calif.; Donald D. Ritchie, New York, NY.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

221 Filed: Oct. 25, 1974 211 Appl.No.:5l8,ll2

OTHER PU BLlCATlONS Chem. Commn. 1968, pages l394l396 The Constitution and Synthesis of Obtusaquine Gregson et 211.

[Ill 3,925,558

[ 1 Dec. 9, 1975 NRL Report 7416-A Preliminary Investigation of Baltman et al. -June 28, 1972.

Tetrahedron Letters No. 2i (l972)pp. 2149-2152- Phenolic and Quinoidal Retusa" Jurd et al.

Primary Examiner-Albert T. Meyers Assistant Examiner-D. W. Robinson Attorney, Agent, or Firm-R. S. Sciascia; Arthur L. Branning; Thomas McDonnell {57] ABSTRACT A fungicide which contains obtusaquinone,

OCH

A method of controlling marine fungi by which obtusaquinone of the above formula is applied to the material to be protected.

2 Claims, 4 Drawing Figures US. Patent Dec. 9, 1975 Sheet 1 01'2 3,925,558

- SOLVENT CONTROL 90 common.

3lppm 80 E 63ppm LIJ E F/G/ o 30 SOOppm ZOOppm O I i TIME(DAYS) FIG: 2

COLONY DIAMETER (mm) US. Patent Dec. 9, 1975 Sheet 2 of2 3,925,558

PESTALOTIA El =SOLVENT CONTROL 0 NORMAL CONTROL CONCENTRATION (ppm) FIG 3 FIG. 4

CHAETOM l UM SOLVENT CONTROL Cl 0 =NORMAL CONTROL CONCENTRATION (ppm) USE OF OBTUSAQUINONE AS A FUNGICIDE TO CONTROL WOOD-INHABITING MARINE FUNGI BACKGROUND OF THE INVENTION The invention relates generally to biological effecting compounds and more particularly to fungicides.

Fungal infestation of wood structures in the marine environment is damaging in two ways. Directly, fungi cause, in time, serious deterioration of the wood structure. But more importantly evidence indicates that fungal infestation is prerequisite for attack by more destructive organisms such as marine borers. The resulting damage to marine wood structures amounts to millions of dollars per year.

Fungicides are divided into two general classes which are referred to as protective and eradicant. The former is applied before the fungus appears and serves to kill or inhibit its growth as it arrives at the treated material. Eradicant fungicides are used to destroy or eradicate fungi which have already located and are actively growing. The major differences in charateristics between the two are that the protective fungicide must, in addition, be extremely stable and persistent.

These additional properties are particularly important for protective fungicides to be used on wood structures in a marine environment. The water and its motion act to leach out all of the currently used fungicides. Whole creosote which is forced under pressure into the interstices of the woody tissue is the most widely used preventative against marine biodeterioration. However, leaching causes the protection provided by this and other techniques to be temporary and variable. This is especially so in tropical and subtropical waters.

Often creosoted timer must be replaced every 4 or 5 years.

Besides the frequently unsatisfactory results, protectants currently being used are also objectional from the pollution caused by their leaching from the wood. All of the standard wood treating compounds, such as creosote and chromated copper arsenate are toxic chemicals. Furthermore, the quantity of the fouling chemicals being introduced into the water is objectionably. This is especially true with creosote. Since the amount of protectant which is impregnated into the wood amounts to 2 to 5 weight percent of the wood and since creosote is its own solvent, the amount of creosote which leaches out is considerable. Also, creosote percolates down the conducting vessels of the wood. Thus, in time, a significant amount collects at the bottom of the timber and exudes into the surroundings.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a wood protectant.

A further object of this in vention is to provide a powerful fungicide.

A still further object of this invention is to provide a fungicide which possesses decreased toxicity to large mammalia and plants.

And a still further object of this invention is to provide a fungicide which is highly resistant to leaching.

Another object of this invention is to provide a method for preventing the infestation of marine wood construction by marine borers.

Another object of this invention is to provide a method of protecting wood from fungal attack.

2 These and other objects are achieved by contacting the material to be protected with obtusaquinone.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the average colony diameter (minimum distance across each colony) as a function of colony age for Pestalotia Oxan thi.

FIG. 2 shows the average colony diameter (minimum across each colony) as a-function of colony age for Chaetomium olivaceum.

FIG. 3 shows the growth rate of the Pestalotia oxanthi colonies as a function of obtusaquinone concentration.

FIG. 4 shows the growth rate of Chaetomium olivaceum colonies as a function of obtusaquinone concentration.

DETAILED DESCRIPTION OF THE INVENTION The fungicide of the present invention may be easily produced by the method disclosed in Gregson et al,

The Constitution and Synthesis of obtusaquinone, A

mm Hg for about l hour, introducing an obtusaquinone solution into the evacuated working chamber of the impregnating device, subjecting the chamber to about 100-125 psi nitrogen for about an additional hour, releasing the pressure, allowing the panels to remain submerged in the solution for 15 minutes to allow pressure equilibration with the interior of the wood, and placing the timer under a vacuum and heat in order to remove excess solvent.

Suitable solvents for the obtusaquinone solution are polar organic solvents such as acetone and ethanol, but

the preferred solvent is acetone. The solution concentration for the above process may be from about 2 weight percent to the maximum solubility of obtusaquinone in the selected solvent.

For woods other than the soft Southern yellow pine, the pressures and times would be adjusted accordingly. The process must be sufficient to impart at least an inch of penetration which can be easily determined by visual insepction for the obtusaquinone imparts a distinctive orange coloring to the wood.

For other applications not requiring a deep penetration of the fungicide, less stringent methods would suffice. Spraying or misting of the fungicide would be used, for example, on surface wood or for non-wood applications.

The following experiments are given to demonstrate the inhibitory effects of obtusaquinone on the growth rates and reproduction of two marine fungi. The tests and the results are not intended to limit, in any manner,

the scope of the instant invention or the claims to follow.

Organisms used in these tests were the ascomycete Chaetomium olivaceum Ames and an imperfect fungus which is morphologically similar to Pestalotia oxanrhi, which hereinafter are referred to as Chaetomium and Pestalotia. These are facultative fungi. They were originally isolated from wood panels exposed in Panamanian estuaries. Cultures were maintained on a glucoseyeast-extract medium (GYE) containing Czapeks salts. The exact composition of the medium is given in Table I.

Table I Composition of the medium used to prepare the assay plates obtusaquinone was incorporated into the culture medium at five concentrations by dilution of an acetone stock solution containing 0.01 gram solute/ml. The solute concentration of each acetone dilution was such that ml of each dilution when added to 200 ml of the culture medium (distilled water containing the inorganic salts) provided a final solute concentration in the culture media of 500, 200, 125, 63, and 31 ppm, respectively. obtusaquinone is very insoluble in water and formed a greenish-yellow precipitate when each acetone solution was added to the aqueous solution. The acetone solution and the salt solution were mixed in a high-speed blender for 2 minutes to reduce the size of the precipitated particles of obtusaquinone and to disperse the compound uniformly in the medium. Most of the acetone was purged from the mixtures by intermittent, gentle heating for 10 minutes and by letting them stand for several hours afterward. To determine whether residual acetone in the medium affected fungal growth, an acetone control was prepared in addition to the control composed of nutrient medium only.

At this stage of preparation the media containing the various concentrations of obtusaquinone and of the controls were at pH 4.1 to 4.2. The media for each concentration were completed by the addition of glucose, Difco yeast extract, and agar before sterilization in an autoclave for 20 minutes at psi. During sterilization the media containing the obtusaquinone turned reddish brown while the controls remained colorless. Cooled media were poured into sterile Petri dishes, and each dish was inoculated in the center with a small uniformly-sized agar block cut from a lO-day-old culture of Pestalotia or Chaetomium. The inoculated plates, prepared in triplicate for each concentration, were incubated at 23C.

The fungal colony on each plate formed a nearly circular disk growing outward from the center. The minimum distance across each colony was the criterion of growth and was measured daily beginning 3 days after inoculation and continuing until the control colonies had reached the outer edges of the plates. For the fastgrowing Pestalotia this limit was reached seven days after inoculation; for the slowgrowing Chaetomium, measurements were continued until the 14th day after inoculation. After growth measurements were discontinued, plates were kept under observation to determine the reproductive activity of the fungi.

All final pH measurements were made four weeks after inoculation of the plates. At this time the average pH of all the Pestalotia plates was about 7.0. The average pH of the Chaetomium plates at the lower concentrations of obtusaquinone was 8.0; that for the higher concentrations was 6.0. Since Chaetomium grows best in acid media, an increase in pH contributed to a decrease in growth rate with time. Also, the slow growth of Chaetomium allowed time for the accumulation of the usual growth-inhibiting factors associated with fungus cultures in the Laboratory, i.e., drying of the agar, formation of metabolic by-products, and relative reduction of living space. These factors were not apparent and did not significantly affect the more rapidly growing Pestalotia cultures. The experiments did have a number of minor inconsistencies. Two minor inconsistencies were noted about the growth of Pestalotia on the media containing the two highest concentrations of obtusaquinones and the growth of Chaetomium on the media containing the two lowest concentrations. Nonhomogeneous dispersion of the compound throughout the media may have contributed to these anomalies, but it was not possible to determine precisely what caused them.

The test results are given in FIGS. 1 through 4. The day-by-day colony diameter (averaged from three identical culture plates) for each concentration of obtusaquinone is presented graphically for Pestalotia in FIG. 1 and for Chaetomium in FIG. 2. The average growth rate for Pestalotia is presented in FIG. 3, and that for Chaetomium in FIG. 4. On FIGS. 1 and 2 the control and solvent control curves are quite similar, the differences being within the limits of experimental error. This fact indicates that trace amounts of residual acetone in the media did not significantly affect the growth of either of the two organisms.

in summary, obtusaquinone had an inhibitory effect upon the vegetative growth of both fungi, even at the lowest concentrations. Generally, the growth rate was reduced as the concentration of obtusaquinone in the medium increased until a threshold value of about 200 ppm was reached for Pestalotia; beyond this an increase in toxicant concentration did not significantly increase inhibition throughout the duration of the experiment. A similar threshold concentration of about 200 ppm obtusaquinone also occurred for Chaetomium. At the highest concentrations obtusaquinone in the culture media had a retarding effect on the reproduction of the tested fungi. Within a week after in oculation, Pestalotia was producing masses of black pycnidia and conidia on all plates except those containing 200 and 500 ppm obtusaquinone. At these higher concentrations, pycnidia and conidia appeared only on the tiny agar cubes which were used for inoculating the plates. Even at the end of 3% weeks no reproductive structures were produced except on the cubes. Conidium production was only slightly reduced at ppm obtusaquinone, and at the lower concentrations it was apparently unaffected. In those cultures of Chaetomium containing obtusaquinone at concentrations of 3l and 63 ppm, perithecia were present after 17 days. At concentrations of 125, 200, and 500 ppm, perithecia appeared on the inoculating cubes, but in much smaller numbers than on cubes in the other cultures of this organism. At the end of 3% weeks there were still no perithecia on the medium beyond the cubes. Possibly enough of the inhibitor diffused into the inoculating cubes to affect perithecium production.

The persistence of obtusaquinone in soft Southern yellow pine was tested by a number of techniques. First, 2 inch pine discs impregnated with obtusaquinone were placed in a vacuum oven at 50C and at a vacuum of less than 5 mm Hg for 8 hours without any measureable loss of the compound. in the second test,

discs similar to those above were subjected to a stream of sea water flowing at a rate of 2 cu. ftJmin for over one year without any noticeable loss. The third test determined that the solubility of obtusaquinone in artificial water to be less than ppm.

As the test results show, obtusaquinone has a powerful inhibitory effect upon the growth rate and reproduction on certain marine ,fungi and has great persistence in wood. These characteristics coupled with the probable sequential relationship between fungus and other marine pest infestation of wood and the marine borer irradicant capability of obtusaquinone make the fungicide of this invention an excellent alternative to creosote in a marine environment.

ing of acetone and ethanol.

Q l I 

1. A METHOD OF TREATING WOOD FOR PREVENTING GROWTH OF FUNGUS WHICH COMPRISES IMPREGNATING A FUNGICIDAL AMOUNT OF OBTUSAQUINONE INTO SAID WOOD.
 2. The method of claim 1 wherein the obtusaquinone is dissolved in a solvent selected from the class consisting of acetone and ethanol. 